[PATCH v2] ACPI: Fix resource_lock dead lock in acpi_power_on_device

[Aaron Lu <aaron.lu@intel.com>]

Commit 0090def("ACPI: Add interface to register/unregister device
to/from power resources") used resource_lock to protect the devices list
that relies on power resource. It caused a mutex dead lock, as below

    acpi_power_on ---> lock resource_lock
      __acpi_power_on
        acpi_power_on_device
          acpi_power_get_inferred_state
            acpi_power_get_list_state ---> lock resource_lock

This patch adds a new mutex "devices_lock" to protect the devices list
and calls acpi_power_on_device in acpi_power_on, instead of
__acpi_power_on, after the resource_lock is released.

Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
---
v2:
If power resource is already on, no need to check if device needs
to be resumed.
v1:
By Lin Ming.

 drivers/acpi/power.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/drivers/acpi/power.c b/drivers/acpi/power.c
index 215ecd0..3582a26 100644
--- a/drivers/acpi/power.c
+++ b/drivers/acpi/power.c
@@ -105,6 +105,7 @@ struct acpi_power_resource {
 
 	/* List of devices relying on this power resource */
 	struct acpi_power_resource_device *devices;
+	struct mutex devices_lock;
 };
 
 static struct list_head acpi_power_resource_list;
@@ -223,7 +224,6 @@ static void acpi_power_on_device(struct acpi_power_managed_device *device)
 
 static int __acpi_power_on(struct acpi_power_resource *resource)
 {
-	struct acpi_power_resource_device *device_list = resource->devices;
 	acpi_status status = AE_OK;
 
 	status = acpi_evaluate_object(resource->device->handle, "_ON", NULL, NULL);
@@ -236,19 +236,14 @@ static int __acpi_power_on(struct acpi_power_resource *resource)
 	ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Power resource [%s] turned on\n",
 			  resource->name));
 
-	while (device_list) {
-		acpi_power_on_device(device_list->device);
-
-		device_list = device_list->next;
-	}
-
 	return 0;
 }
 
 static int acpi_power_on(acpi_handle handle)
 {
-	int result = 0;
+	int result = 0, resume_device = 0;
 	struct acpi_power_resource *resource = NULL;
+	struct acpi_power_resource_device *device_list;
 
 	result = acpi_power_get_context(handle, &resource);
 	if (result)
@@ -264,10 +259,26 @@ static int acpi_power_on(acpi_handle handle)
 		result = __acpi_power_on(resource);
 		if (result)
 			resource->ref_count--;
+		else
+			resume_device = 1;
 	}
 
 	mutex_unlock(&resource->resource_lock);
 
+	if (!resume_device)
+		return result;
+
+	mutex_lock(&resource->devices_lock);
+
+	device_list = resource->devices;
+	while (device_list) {
+		acpi_power_on_device(device_list->device);
+
+		device_list = device_list->next;
+	}
+
+	mutex_unlock(&resource->devices_lock);
+
 	return result;
 }
 
@@ -353,7 +364,7 @@ static void __acpi_power_resource_unregister_device(struct device *dev,
 	if (acpi_power_get_context(res_handle, &resource))
 		return;
 
-	mutex_lock(&resource->resource_lock);
+	mutex_lock(&resource->devices_lock);
 	prev = NULL;
 	curr = resource->devices;
 	while (curr) {
@@ -370,7 +381,7 @@ static void __acpi_power_resource_unregister_device(struct device *dev,
 		prev = curr;
 		curr = curr->next;
 	}
-	mutex_unlock(&resource->resource_lock);
+	mutex_unlock(&resource->devices_lock);
 }
 
 /* Unlink dev from all power resources in _PR0 */
@@ -412,10 +423,10 @@ static int __acpi_power_resource_register_device(
 
 	power_resource_device->device = powered_device;
 
-	mutex_lock(&resource->resource_lock);
+	mutex_lock(&resource->devices_lock);
 	power_resource_device->next = resource->devices;
 	resource->devices = power_resource_device;
-	mutex_unlock(&resource->resource_lock);
+	mutex_unlock(&resource->devices_lock);
 
 	return 0;
 }
@@ -719,6 +730,7 @@ static int acpi_power_add(struct acpi_device *device)
 
 	resource->device = device;
 	mutex_init(&resource->resource_lock);
+	mutex_init(&resource->devices_lock);
 	strcpy(resource->name, device->pnp.bus_id);
 	strcpy(acpi_device_name(device), ACPI_POWER_DEVICE_NAME);
 	strcpy(acpi_device_class(device), ACPI_POWER_CLASS);
-- 
1.7.12.21.g871e293